Manufacture of isobutylene



Reissued Aug. 15 1950 UN lTED STATES PATENT OFFICE; a v 23,254 MANUFACTURE OF ISOBUTYLENE William 0. ffutt, Oakmont, Pa", assignor to Gulf Research &' Development. Company, Pittsburgh, Pa., a corporation ofDelaware No Drawing. Original No. 2,498,999, dated February 28, 1950, Serial No. 750,641, May 26, 1947..

Application for 166,969

2 Claims reissue June 8, 1950, Serial No.

Matter enclosed in heavy brackets appears in theoriginal patent but forms no partof this 1 reissue specification; matter printed in italics indicates the additions made by reissue This invention relates to the manufacture of isobutylene, and more particularly .to the depolymerization of isobutylene polymersto yield isobutylene.

In the production of high molecular weight b employed in accordance with my invention. have polymers from isobutylene, it is essential to ema low cracking activity index, thatis', the crack-' ploy substantially pure isobutylene as a starting ing activity of my catalysts for the conversion material, as otherwise it is difficult if not imposof hydrocarbon oils into gasoline is so low as to sible to secure the desired high molecular weight be uneconomical for that purpose. However; polymers. In the production of tertiary butyl when in this condition, the catalysts are adphenols by alkylation of the phenols with isobutylene, it is also desirable to employ substantially pure isobutylene. Since the isobutylene available in the petroleum industry, for example from refinery gases and gases obtained by dehydrogenating butane is usually contaminated with normal butylene and butane, it is necessary to' separate the isobutylene. One such method comprises the selective polymerization of isobutylene predominantly to dimer. This is done by passing the mixed gases containing isobutylene and normal butylenes thru 60 to 70% sulfuric acid at room temperature, whereby the isobutylene is selectively absorbed. Upon heating the sulfuric acid containing the isobutylene to a temperature around 100 C., the isobutylene polymerizes predominantly to the dimer, with smaller amounts of codimers, and trimers. This polymer mixture is then subjected to thermal decomposition at elevated temperatures, preferably in the presence of a natural clay catalyst such as fullers earth, bentonite, or the like.

A serious defect of the process heretofore described has been the short active life of the catalysts. The rapid deactivation of such catalysts with the consequent need for frequent replace ment has rendered this process unduly difficult and costly.

This invention has as an object, therefore, a process for the depolymerization of liquid isobutylene polymers wherein the catalyst possesses a long active life. v

A further object of this invention is to provide a catalyst for the depolymerization of isobutylene dimers which is capable of giving high yields of virtually pure isobutylene. Other objects will appear hereinafter.

These objects are accomplished by the present invention wherein a liquid isobutylene polymer to be depolymerized is'passed at an elevated temsurface active silica-alumina having a low crack ing activity index.

As stated, the synthetic silica-alumina catalysts f catalytic activity and the capacity for repeated regeneration to remove carbonaceous deposits. Thus, I have found that a catalyst of the type described in Example 1 of U. S. Patent 2,283,173

resulting from the deposition of carbonaceous materials on the catalyst, but refers to the con-- dition of thecatalyst after repeated conversion cycles,- including regeneration to burn off carbonaceous deposits.

Other synthetic surface active silica-alumina catalysts may also be employed, it being immaterial how the catalyst is made provided it is a synthetic surface active silica-alumina, catalyst and has a low cracking activity index. Although the use of catalyst discarded from the catalytic cracking of hydrocarbon oils is an advantageous feature of my invention, other methods may be employed to reduce the activity of the catalyst. Thus the cracking activity of the catalysts may be reduced to the desired point by subjecting the catalyst to a steam treatment. A suitable method for reducing the activity of the catalysts by treating with steam comprises exposing the catalyst at a, temperature of 1300 F. for a period of four hours to steam at atmospheric pressure.

The desired low[er] cracking activity'of'the catalyst may be determined quantitatively 'by measuring the cracking ac ivity d x i the,

catalyst. By cracking activity index, I refer to the volume per cent of 400 F. end-point gasoline obtained by cracking a standard East Texas gas oil under standardized conditions which comprise a temperature of 800 F., a liquid hourly space velocity of 1.5, and a ten minute cycle in the presence of 200 cc. of the particular catalyst being studied. The East Texas gasoil employed. has the following inspection:

Specific gravity 0.8423

Gravity, API 36.5. Sulfur, percent 02137 Aniline point, C 73.4

A. S. T. M. DISTILLA'IION Initial boiling point- 430 480 50% -e 531 90% 636' Endipoint 692 The preferred cracking activity index of the synthetic surface activezsilica-alumina catalysts of. invention is about 28 to- 30, however cracki'ng activity indices, of .22' to 32 may also'be employed.

According to a preferred embodiment of my invention, anisobutylene ,polymen'f or example, one containing about 55% diisobutylene, 115% ccdimer, 5%, light material, and the remainder as. trimer plus tracesof higher polymers ispumped. to. a preheater where the. polymer is heated to a. temperature of about.450.F. The polymer, after passing through the.preheater, enters .a reactor preferably of 'the cylindrical type. The reactor is maintained. at a temperature in the. range. 450 to750'F., preferably 600 to 615 .F.,..and a pres,- sure. whichis substantially atmosphericorslight- 1y higher. The reactor is filled with alow cracking activity synthetic silica-alumina catalyst, suchas described here'inabove. The particle size of. the. catalyst .is-about 4-.6, mesh. However, the size-of. the catalystis notcritical, but the larger size avoidsiexcessivepressure. drop through. the reactor. Thelliquidhour'lyspace velocity through. the reactcrisof theorder of 0..-.5..to.l.0, and.is,pref-- erably aboutfllfi- After. passing through the re material passes to :a fractionating columnirom. which .pure .isobutylene .is separated. overhead. .After an extended ,period carhona-. ceous materialis .depositedcnthe catalyst to .such anextentasitoredum the. dfip lylmerizing activity. Itis. a reaturecf this inventi'on that re peated burn-offs of such carbonaceous deposits with anoxygen containinggas, .suchtasair. taregenerate. the catalyst. are ndt harmful to. .the; life or activity of the catalysts ior .depdlymerization. of. the isobutylene, polymers.

"The forllowingresults were obtained using the iscbutylene {polymer .and catalyst heretofore described] At 6,'75-.E. and aspace velocity of 0. &33

4 the presence of synthetic surface active silicaalumina catalysts having a low cracking activity index results in high yields of virtually pure isobutylene, with negligible deposition of carbonaceous materials on the catalyst. However, when the removal of carbonaceous deposits becomes necessary or desirable, burning-cit. may be accomplished repeatedly without. destroying the activity or shortening the life of the catalysts. Furthermore, the catalysts have a long active life and are mechanically stable, thus obviating the necessity for the frequent [frequency] catalyst replacement characteristic of prior art catalysts.

What. Ixclaim l. A process for. depolymerizing a liquid polymer comprising essentially isobutylene dimer which comprises. passing said polymer at a temperature offrom 450 to 750 F. over a catalyst comprising a synthetic surface active silicaalumina having a cracking activity index of from 22120 32-, said cracking activity index being the volume percent of; 400 F. .encl-peintgasoline obtained by cracking an East Texasgasoil at a temperature of 800 F., a liquid hourly space velocity of 1.5 and a ten minute; cycle in the presence of 200 cc. of .saidcatailyst, the Eastv Texas; gas oil havingqa. gravity ,cf':36.'5 .API and an A..;S. distillation as tol'lows'z;

2. A process for .depolymerizing a liquid ;poly-. mer comprising essetially isobutylene'dimer which comprises qpa-ssing said polymfir at atemperature of hem-600 to. 6 75-E. and at a liquid hourly space velocity =.of about 0.8 over a :catalyst comprising .a synthetic surface active. silica-alum-ina having a cracking activity index-cf 28 to. .30, and recover-- ing theisobutylene formed thereby-,.-said cracking activity index beingthe volume per-centpof $00? endpoint gasoline obtained .by cracking. .a-n. East, Texas-g-asoil-ataitemperaturecf .800- a liquid hourlyspace velocity of .-1-.5 and-atenminutecycle. in-.-the presence of 200 ;cc..:of.sai'd. catalyst, the East Texas gas oil having a ig iavity of 36.5 ".API and. an A. .S. T.. ;M.-;distil-lation as follows Initialboiling point, 43,0 10% H "[400] 48.0 :50.% i 531 636.

Endpoint. 6921 WILLIAM c. OFFUTT.

MEERENfiES CITED The. following .reienenc'es. are.- of record in. the file oflth'is or the original patent;

UjNI-TED STATES PATENTS 

